This invention relates to numerical control systems for processing machines such as eroding machines, in which the processing machine includes a tool and means for holding a workpiece, and in which the control system comprises means for positioning one of the holding means and the tool with respect to the other in at least two dimensions, as well as means for determining movements of the positioning means along a path adapted to accomplish a desired treatment process at a treated surface of the workpiece.
In eroding machines of the type described above, it has become customary to widen the contour formed by a cylindrical electrode in the workpiece for example by lowering the electrode into the workpiece along the direction of the cylinder axis of the electrode. This contour is widened by a so-called planetary movement (for example a circular movement between the workpiece and the tool in a plane perpendicular to the cylinder axis of the tool).
In the past, it has been common practice to control this planetary movement and the oscillations of the electrode with respect to the workpiece necessary for the erosion process in order to adjust the eroding gap between the electrode and the workpiece. One prior art approach is to use the three axis positioning system of the machine table which supports the workpiece in order to achieve the desired separation between the tool and the workpiece. This approach to controlling rapid oscillations is, however, unsatisfactory in many applications because of the relatively large mass and inertia of the machine table.
Furthermore, it is a known practice in eroding machines to control the planetary movement and the adjustment of the erosion gap by suitably positioning the electrode along three secondary axes. With this approach, however, a relatively large capital expenditure is required for the numerical control system.